Bulk GdBCO–Ag superconductors with holes

Abstract

Bulk single-grain GdBCO-Ag superconductors with and without holes grown using a top-seeded melt-growth process are analyzed. The levitation force at 77 K is higher for the sample with holes. From the performed complex microstructural analysis, we were able to assess the positive, negative, or neutral contribution of the analyzed microstructural elements in the studied samples. It turns out that the macroscopic superconducting properties can be negatively affected by defects arising during the absorption of the holes by the growth front of the crystal. Other microstructural features, such as a higher volume fraction of Gd 2 BaCuO 5 (Gd211) in the a-growth sector (GS) than in the c-GS and the presence of tetragonal regions of GdBa 2 Cu 3 O 7−x (Gd123) are similar in both samples and cannot significantly affect the observed difference in macroscopic superconducting properties. In terms of macroscopic superconducting properties, in our opinion the most important is the lower porosity of the a-GSs in the upper part of the sample with holes.